In response to consumers' demands, the currently designed electronic and communication products all are small in volume, light in weight and powerful in function.
However, to meet the above requirements in design, the currently available electronic and communication products also have densely arranged high-frequency clock electric circuits. This condition inevitably worsens the electromagnetic radiation problem and results in electromagnetic interference (EMI) among different electronic products or even has bad influence on users' health.
In the past, engineers tried to solve the problem of electromagnetic radiation with specially designed and planned circuits. This solution, however, requires relatively long time and high cost to achieve the purpose of EMI prevention. To overcome the above disadvantage, a new way has been developed recently to use a shielding film on the electronic product to shield electromagnetic wave. Since the shielding film has the advantage of being convenient to use and low in cost, and it is not necessary to re-design the products for using with the shielding film, the shielding film has been quickly and widely adopted by the electronic industry for EMI prevention.
According to the principle of the shielding film, shielding layers having good electric conductivity are attached to upper and lower surfaces of electronic working elements in the electronic product and are electrically connected to the grounding circuit of the product. When the electromagnetic radiation reaches the shielding layer, an electromagnetic interaction occurs, and electromagnetic energy is absorbed by the grounding circuit, so that the shielding layer has the effect of shielding electromagnetic radiation.
The electric conduction between the shielding layer and the grounding circuit of the electronic working elements has direct influence on the electromagnetic shielding effect of the shielding layer. When the grounding circuit has a relatively small contact resistance while the electromagnetic interaction is relatively strong, better shielding effect can be obtained.
FIG. 1 shows the structure of a conventional shielding film 1 includes an insulation layer 11, a shielding layer 12 and a conductive adhesive layer 13. The insulation layer 11 stops the conductive shielding layer 12 from contacting with electronic elements. The conductive adhesive layer 13 includes an adhesive agent having conductive particles 13a added thereto. The conductive particles 13a electrically connect the shielding layer 12 to the grounding circuit of the electronic elements, and the conductive adhesive layer 13 is heat cured. With these arrangements, the shielding film 1 can be fixedly attached to electronic elements to achieve the purpose of shielding electromagnetic wave.
However, in the conventional shielding film 1 shown in FIG. 1, while the conductive adhesive layer 13 having the conductive particles 13a added thereto can provide bonding and electrical conducting functions at the same time, the large contact resistance among the conductive particles 13a tends to result in lowered electric conduction and accordingly indirectly affects the intended shielding effect. Further, the size uniformity, the degree of dispersion and the settling of the conductive particles 13a all have influence on the electric conduction and the adhesion of the shielding film 1 to thereby lower the shielding effect thereof.
In view of the disadvantages in the conventional shielding film, it is desirable to develop an improved shielding film having excellent electromagnetic shielding function and a method for efficiently manufacturing such shielding film through simplified procedures at reduced cost.